A stereotypical Asian way to say "yes," no doubt featured in Charlie Chan movies and other instances where the foreigner uses his language only to say words that he'd have learned FIRST in English.

Yes, No, Please, Thanks, Hello, Goodbye — those are the first things you learn in a foreign tongue, so to demonstrate that Poirot is a native French speaker, he fails to use those very words in English, when in reality it's the more complicated locutions that he'd stumble over.

Yes, I know. It's for the audience, who knows what Merci and Adieu mean. It's still lame.

Actually it's only loosely stereotypical in that it is actually Japanese for something like I See, or That is so, rather than being fake generic Asian.

Use it myself on occasions, but then in my area not only are there are a lot of Japanese and Americans with Japanese DNA, but a friend in the latter category has stated that he considers me to be Japanese, and my DNA is Scottish, Scottish, Scottish, British isles mutt . . . . .